I have been wondering about the 8828B fan. When roasting with the fan on, there is often a lot of smoke coming out of the bean hopper if the cover is opened up. If the rear filter is taken out, the smoke coming out of the hopper (at the top) stops and the fan speed increases. Also, the temperature of the air coming out of the fan with the filter in is quite cool (luke warm) but with the filter out the temperature is very warm.

This seems to tell me that the fan with the filter isnt doing a good job of evacuating the smoke from the drum. Having the smoke evacuated would seem to be a good thing as this is a critical aspect of commercial drum roasters, from what I have read, to avoid the beans tasting like smoke.

I dont understand why there is a temperature change with the filter removed, however.

Can someone shed some light on this? It appears that the fan is more effective with the filter removed. More smoke is exhausted without the filter but thats ok for me because my overhead fan sucks it up and out.

If its a matter of changing the bean temperature, thats ok because it just means adjusting the profile to accommodate. I'd rather have effective smoke exhaust.

But maybe I am missing something.

Excellent topic for a 1st post I don't recall seeing many convincing discussions on the HT fan.

I think what you lose with the filter out is finer control of air flow; i.e. 25% fan without the filter would equal 100% fan with the original filter (or some other equation, linear or not!).

That said, maybe other filter materials will give us a better air flow control range than with the original filter or without any filter at all. Truth is, I'm still not sure how important fan control is on the HT, I know "fan on" is useful for getting humidity & smoke out but not sure how better air flow control would affect a HT roast. Maybe some guru HT-B/P roaster would care to clarify?




EDIT: re-reading your post, I hope this reply was on topic. If not, please accept my apology.

I will comment based on my preferred opeation of the "B" model which is to do manual roasts, with me in control of fan and tempoerature changes as wel as when to add the beans. I program max time and max temp, and I roast 300 grams of coffee, adding the beans at about 250 F. (not when the roaster tells me to).

I am not privy to the intricacies of the programming so can't say why they turn the fan on in auto modes when and how they do. As an anecdotal data point, with the KN-8828B to get a fast roast (shorter time with larger capacities), using the stainless steel permanent 120mm computer fan, I had to block off about 60% or so of its area because there was too much heat loss with that free flowing filter.

I will relate what I do when roasting manually- I emulate the default program by turning on the fan for about 15 seconds at around 275 to 300 degrees to clear humidity that builds up earlier. Then I leave the fan off until I see a bit of smoke coming from the top filter and/or the bean loading chute. At that point I turn the fan on at 25%. At about 375 or so when the smoke increases I turn the fan on at 50% for the remainder of the roast. I use the smoke as an indicator as to how high and when to turn on the fan. Additionally, depending on the age of the stock filter you may need to change your "normal" fan speed to compensate.

The bottom line for me is that the main function of the fan is to keep the roast chamber's humidity and smoke level to a minimum. Its secondary function can be used to fine control (or fast control) temperature changes. Other than that, in terms of critical control, I do not see the fan as being a critical component of the roaster's operation.

When I am roasting in the HT, even with the fan at 100% (filter in) There is a lot of smoke billowing out of the bean chute. This tells me that there is a lot of smoke in the drum. This is not good as smoke will flavour the coffee (with smoke). If I look in the drum with a flashlight, I dont see any smoke, so its odd. Perhaps the smoke is just not thick enough to reveal with a flashlight? Removing the filter causes the billowing smoke to completely stop. This is the mode I want to see. So I guess I will experiment with roasting without the rear filter in because I want to see maximum smoke evacuation. The temperature will tell me if there is too much airflow, causing a decrease in temperature. Who knows, maybe it will work.

I am thinking that the fan/filter combo is mainly there to reduce the amount of smoke to the outside. afterall, a smokey roaster is going to get bad press and people wont buy it. so perhaps it was done as trade-off to meet market demand rather do the right thing for the roast which is get rid of the smoke in the drum?

plexus wrote:When I am roasting in the HT, even with the fan at 100% (filter in) There is a lot of smoke billowing out of the bean chute..........

It might be time to change the filter...? Or maybe clean the fan? Remove the fan and check the blades- if they are crudded up with particulate matter it will definitely decrease its efficiency. I have actually washed my fans with TSP, gently scrubbing the blades with a brush and rinsing them well under a running faucet, then blowing them dry with compressed air while holding the blade from spinning. Not recommended in the manual, and certainly not covered by the warranty, but it has worked for me.

The filter is to remove as much particulate matter from the smoke as possible as this is the component that can cause breathing problems and allergic reactions, and it removes the moisture/oils/etc./? from the smoke so that it minimizes the mess to clean up. I roast outdoors anyway so it doesn't matter. The filter also "regulates" airflow so that it balances the need to keep the roast chamber smoke free with a minimum of heat loss, all while filtering as much of the particulates as possible.

I have only done about 8 batches in the hottop so i dont think the filter needs to be changed. maybe it doesn. no matter, i just did an experiment with a roast using no filter. or rather, i just pulled the filter up so that it was still in the machine but not in the stream of the fan.

the results were great. first of all, there was much smoke being evacuated from the drum. this is what i want. with the filter in place, there is still a lot of smoke in the drum as can be seen coming out of the chute at the top if you remove it. with the filter out of the stream of air, the smoke coming out of the top is eliminated. i ran the fan on 1 through the roast and you could see the smoke being blown out. also some chaff was blown out as well. thats fine. the temperature was still going up and i didnt notice any appreciable elongation of roast time with the fan running on 1.

i just left the fan on 1 because it seemed it was doing a good job of evacuating the smoke.

shortly into the second crack i ejected. another nice thing was that instead of a lot of smoke coming from the ejected roast, which my oven fan has a hard time evacuating, there was none. it seems like the filter removed from the hottop creates enough suction through the bean eject chute to suck the smoke out through the hottop and out through the back. this worked great as the smoke was easily sucked up through my oven overhead fan. the net result was less smoke in the kitchen in general.

so i am not seeing any benefit to using a filter on the hottop. it seems to do a better job without it. also the roast was just gorgeous and seemed more consistent than what i've done in the past. maybe this was a bean issue more-so than the fan.

so... not sure about the filter in this roaster. comments?

I now use a SS mesh filter that was intended for a computer. Before making the switch, I, too, had a lot of smoke leaking from the bean chute cover. Now, there is none. A big improvement in my book.

Jim

I would advise against removing the fan, as that will likely cause too much airflow and longer roast times. As Randy indicated, reducing the airflow through the filter with his filter mod allowed for shorter roast times with higher batch sizes.

I have not noticed any significant difference in the cup based on lower fan speeds and more smoke coming out of the bean chute or top filter (I lowered fan speeds to reduce the intake of cold air during very cold roasting sessions).

As far as temperature control with the fan, what I've found troubling so far since my installation an ET thermocouple is that too much reliance on fan to slow down/lengthen the roast after 1st crack tends to drop the ET, which could cause problems with the surface reactions on the beans. I've not confirmed whether this is or is not a significant problem with the hottop and the beans I've roasted, but I plan to conduct tests to see if profiles like this





show superior results in the cup compared to something like this

Great thread you have started here Brett. Actually I have been thinkin about this my self as well. Especially I have never been able to roast a really dark roast without getting a smokey taste in the cup.

well, there you go. i really do think that the fan filter is there to strike a balance between drum roasting and making the hottop viable for your average consumer. i dont think running it without the filter is such a bad thing, it will evacuate smoke even on the low setting. i will have to do some timing to see how this might affect roast time. you dont really need to turn it on until just before 1st crack. also i dont see how putting in a less restrictive filter like the mesh screen idea is going to make that much of a difference - its still going reduce airflow restriction. perhaps its just enough to keep the bean temp rising while providing better smoke evacuation. i am experimenting with using a stock filter with the paper part removed or the black material removed. but i am getting the best results just running it with no filter material in the fan flow. i dont want smoke in my drum!